Drive means for reactance unit



y 1963 L. T. BARNES DRIVE MEANS FOR REACTANCE UNIT Filed Oct. 12, 1960 rm 1 //4 l 3 F/G'. Z

INVENTOR.

of an adjustable electrical unit United States Patent ()fifice 3,090,243 Patented May 21, 1963 3,090,243 DRIVE MEANS FOR REACTANCE UNIT Llewellyn T. Barnes, 155 Atlantic Ave., Freeport, NY. Filed Oct. 12, 1960, Ser. No. 62,282 12 Claims. (Cl. 7410.85)

'Ilhe present invention relates to an adjustable electrical reactance unit, and in particular to a miniaturized unit having a movable piston-type of electrode actuated by screw means for use as a trimmer capacitor or the like and especially adapted to be secured to a panel, bracket, chassis or other similar support.

In many electronic installations, adjustable electrical reactance units such as those of the trimmer type are widely employed. It is often desirable to conveniently and rapidly secure such adjustable electric reaotance units to a panel, bracket, or chassis. It is therefore one of the important objects of the invention to provide an adjustable electrical reactance unit having means for convenient attachment to a panel or other support and in which there may be obtained very fine and accurate adjustment of the unit with a minimum of backlash. In carrying out the invention there is combined with the mounting means for the adjustable reactance unit, means for assuring fine tuning while eliminating and minimizing accidental creepage or movement of the piston due to shock or vibration. Thus, there is achieved in the present invention a type of mounting which assures a maximum range of reactance, very fine and accurate adjustment of the units with minimal lost motion while permitting the units to be made in a very small size.

It is intended to encompass under the term reactance unit such electrical devices as trimmer capacitors, resistors, inductors and the like.

In my prior application for United States patent, Serial No. 841,301, lfOI Adjustable Electrical Reactance Unit, filed September 21, 1959, of which this application is a continuation-impart, there is disclosed a trimmer capacitor having means for fine tuning, which means are augmerited and employed in the present invention with provision being made to mount the adjustable reactance unit on a panel or the like together with means for further eliminating lost motion.

The concept of the present invention includes the provision of a trimmer type reacta-nce unit having a movable electrode in the form of a piston which slides within a hollow housing. The piston is actuated by a screw which is turnable within an intermediate member which in turn has a screw engagement with the piston. The screw, intermediate member and piston are all telescopically interconnected with one another to move the piston upon turning of the screw. The housing is provided with an end wall which is externally threaded and has a recess for receiving an end of the drive shaft. The end wall is adapted to receive a nut thereon for enabling the device to be secured to a panel or the like while within the recess there is provided means for rotating the shaft so as to assure proper operation of the invention.

An addiitona'l object of the invention is to provide an adjustable reactance unit in which the piston and interior of the hollow body forming the housing are elliptical in shape so as to provide for sliding movement of the piston without rotation thereof, and in addition, provide a maximum effective area of reaotance between the piston electrode and the fixed electrode. 1

Another object of the invention resides in the provision in which adjustment means are provided for varying the frictional drag on the screw threaded elements to thereby produce an optimum degree of fine linear movement of the piston.

Still another object of the invention is the provision of an adjustable reactance unit of the character described 1 erein incorporating improved adjustment means for the piston, the adjustment means being constructed so as to provide the highest approach to linear tuning with ultra fine resolution and a minimum of lost motion.

An important feature of the invention residesin the provision of a split thimble which is positioned about the drive shaft and held in place by a cylindrical member provided with portions complementary in shape to the exterior configuration of the split thimble so as to rigidly hold the split thimble in place. Spring means are provided for continuously urging the cylindrical member into wedging engagement with the split thimble.

It is therefore a further object of the invention to proenable the trimmer capacitor to be conveniently assembled and disassembled and to be easily mounted on a panel, chassis or other support.

skilled person.

Additional objects and advantages of this invention will become apparent during the course of the following specification when taken in connection with the accompanying drawings illustrating a preferred embodiment of the invention and wherein:

FIG. 1 is a perspective view of the trimmer capacitor constructed in accordance with the present invention and illustrating particularly the means for mounting the device on a panel or the like;

FIG. 2 is an enlarged longitudinal sectional view of the adjustable electrical reactance unit and illustrates the piston in its fully extended position; and

FIG. 3 is a vertical sectional view as taken along the plane of line 33 in FIG. 2, illustrating particularly the construction of the split thimble forming one of the important elements of the present invention.

With continuing reference to the accompanying drawing wherein like reference numerals designate similar views, the invention herein is illustrated in an embodiment of a variable condenser of the trimmer type. The condenser is provided with a hollow body Ill made of a material having a relatively high dielectric constant and preferably of a low coeflicient of thermal expansion. Examples of the materials from which the hollow body it] may be constructed are quartz, glass, polystyrene, or the like. The body 10 is preferably of an elliptical or oval cross section, rather than of a circular shape but may be of any suitable shape other than circular as will be hereinafter explained. The hollow body It has fixed to its outer surface an electrode 12 which is preferably in the form of a band of conductive metal bonded to the outer surface of the hollow body 19, or which may be in the form of a silver layer fired on the surface of the hollow body 10.

The hollow body 10 has a bore 14 therethrough of elliptical shape. A movable electrode in the form of a piston 16 which is of a shape conforming to the cross sectional shape of the bore 14 is slidably fitted within the hollow body 10. The piston 16 is provided with an end wall 19 having a circular opening 18 therein and is provided with an internally threaded bore 20 having internal threading as at 22 and forming a shoulder 24 in conjunction with the opening 18.

Drive means are provided for sliding the piston 16 longitudinally within the hollow body 10 and relative to the fixed electrode 12 so as to vary the capacitance of the condenser. The drive means include both an intermediate member 30 and a drive shaft 32. The intermediate member 30 is preferably of a cylindrical shape having an enlarged end portion 34 provided with external threading 36 which is threadedly engaged in a precise manner with the internal threading 22 of the piston 16. The main body portion of the intermediate member 30 is shaped to fit slidably and rotatably through the circular opening 18 in the end wall of the piston 16. The intermediate member 30 itself has an end shoulder 38 which is provided with a circular opening 40 which communicates with a bore 42 extending to the opposite end of the intermediate member 30. The bore 42 is internally threaded as at 44.

The drive shaft 32 extends slidably and rotatably through the end wall opening 40 of the intermediate member 30 and has an integral terminal extension 46 of an enlarged diameter. The extension 46 is located within the threaded bore 42 of the intermediate member and is provided with external threading as at 43 sized to intermesh accurately with the internal threading 44 of bore 42.

The other end of the drive shaft 32 has a portion 50 of square or other non-circular configuration on which a head piece 52 is mounted. The head piece 52 is gen erally of a cylindrical configuration and is provided with a slot or kerf 54 therein for receiving a screw driver blade or the like. Further, the shaft is provided with a pair of peripheral recesses 56 and 58 therein.

The drive shaft 32 is journalled in an opening 60 in an end wall 62 of the hollow body, which end wall is provided with an extension 64 hearing external threading 66. Further, the end wall extension 64 is provided with an internal recess 68 and at its outer end is provided with an internally threaded bore 70 forming a shoulder 72. A nut 74 is threadedly engaged with the internal threads formed by the bore 70 and is provided with portions 76 which are complementary to the tapered truncated conical portions 78 of the head piece 52 so as to wedgingly hold the head piece 52 within the recess 68 yet which complementary surface 76 forms bearing surface for the head piece 52 against which it may ro--v tate. The shaft end 50 is non-rotatably but slidably re ceived within the cavity 79 in the head piece 52.

Disposed about the shaft 32 is a split thirn-ble 80 formed in two pieces 82 and 84 as can be seen best in FIG. 3. The split thimble pieces 82 and 84 are provided with key portions 86 and 88 respectively, which are adapted to sit within the cutout portions 56, 58 of the shaft to keep the split thimble non-slidably and non-rotatably on the shaft 32. The split thimble is provided with a terminal peripheral flange 90 about its parts which is adapted to bear against the interior surface 92 of the end wall 62.

Disposed about the split thimble 80 is a cylindrical member 96 which is provided with a peripheral end flange 100. The split thimble parts are provided with a truncated conical portion 102 and the internal configuration of the cylindrical member 96 is such as to be complementary to the truncated conical portion 102 and therefore to apply wedging action when the cylindrical member 96 is fitted over the split thimble 80. A coil spring 106 engages the flange 100 of the cylindrical member 96 so as to urge the tapered interior configuration 104 of the cylindrical member 96 to engage the truncated conical portion 102 of the split thimble. The spring 106 also engages the shoulder 110 of the head piece 52, thus continuously securely seating the head piece against its bearing surface 76.

The entire trimmer condenser is secured on schematically indicated at 112, which support may be a panel, bracket, frame, or the like. Such attachment is accomplished by means of a nut 114 which is threadedly engaged on the exterior threaded portion of the extena support,

.sion 64 of the end wall 62. A locking collar or washer 116 may be disposed about the extension 64 and bear against the shoulder 120 of the end wall 62, and thus, in cooperation with the nut 114, hold the trimmer condenser in position.

In order to prevent lost motion and slippage as the condenser is adjusted and therefore provide a more accurate tuning control of the condenser, keyhole slots and 132 are cut into the enlarged end parts 46 and 34 of the drive shaft 32 and the intermediate cylindrical member 30 respectively. Set screws 1'34 and 136 are mounted in the end faces of the respective enlarged end portions 46 and 34 and extend into the respective slots 130 and 132 so that when the set screws 134, 136 are tightened or turned inwardly, their ends engage the opposite wall surface defining the respective slots. The screws 134, 136 exert a spreading force on the end portions thereby spreading and enlarging the slots 130 and 132. The spreading force presses, the external threads 36, 4S slightly out of alignment with the respective meshing internal threads 22, 44 and thus creates a drag on the screw threading of the piston, the intermediate cylinder and the drive shaft. Since the set screws 134, 136 are threaded into the rear end surfaces of the drive shaft 32 and cylinder 30', which surfaces face the open end of the hollow body 10, the screws are easily accessible for facilitating adjustment by insertion of a screw driver or other similar tools through the open end of the hollow body 10. In order to assure the smoothest and most efficient adjustment of this device, one of the screws 134 or 136 should be tightened slightly more than the other, in a manner which will be further described in detail.

The piston or movable electrodes 16 is constructed of an electrically conductive material as is the intermediate cylindrical member 30, the drive shaft 32 and the end Wall 62. It is desirable that this conductive material should have a relatively low thermal expansion co-iefiicient similar or identical to that of the dielectric material from which the hollow body 10 is fabricated. It has been found that Invar, an iron-nickel al- 10y, has quite similar expansion characteristics to the body material of the condenser and accordingly the use thereof is preferred. The head piece 52 and the nut 74 may be made of similar conductive material or may be made of a suitable insulative material as may be desired.

A terminal lug 140 is bonded \or otherwise secured by means of a flange 142 to the :outer surface of the electrode 12. A conductive metal band 144 is disposed about the hollow body 10' in contact with the conductive end wall 62 and a second terminal lug 146 is secured thereto. The band 144 makes contact with the end wall 62 and thus with the shaft 32 and movable piston 16.

Of course the terminal lugs 140 and 146 are adapted to be connected in the conventional manner to circuit lead wires. The fixed electrode 12 is energized by the lug 140'. The movable electrode or piston 16 is energized by the lug 146 through the band 144, the end wall 62, the drive shaft 32 and the intermediate cylindrical member 30. In the fully extended position of the piston 16, as shown in FIG. 2 the piston is in registry with the fixed electrode 12 and the unit is in condition for maximum capacitance. In the fully retracted position the piston 16 is completely spaced from the fixed electrode 12 and this position represents the capacitance of the unit.

In describing the operation of the condenser, the set screw 134 is tightened to a greater degree than the set screw 136 so as to impart a greater frictional tension on the drive shaft threading 48 and the internal threading 44 than between the cylinder external threading 36 and the piston threading 22. Accordingly, as the shaft 32 is rotated by rotation of the head piece 52, the intermediate cylinder 30 rotates with it and its external threading 36 turns within the internal piston threading 22. The piston 16, because of its elliptical shape or other suitable noncircular shape, cannot rotate and this screw action therefore moves the piston longitudinally, the piston sliding through the hollow body and towards the right as viewed in FIG. 2, and out of registry the fixed electrode 12, decreasing the capacitance of the unit. As the drive shaft 32 continues to rotate, the piston 16 slides through the hollow body 10 relative to the longitudinal and movable intermediate member 30 and drive shaft 32 until its rear edge comes into registry with the rear edge of the enlarged end portion 34 of the intermediate men A stop plate 160, afiixed to the rear end portion of the piston 16 by means of a screw 162, projects partially across the bore 20 and thus stops further longitudinal movement of the piston 16 relative to the intermediate member because the stop plate 160 engages the intermediate member 30. The piston 16 becomes rigidly coupled to the intermediate member 30 and can no longer rot-ate. Continued turning of the drive shaft 32 now causes meshing of its external threading 48 with the internal threading 44 of the intermediate member 30 Thus, the intermediate member 30 is moved longitudinally to the right as viewed in FIG. 2. The intermediate member will carry the piston 16 until the latter reaches its fully retracted position in which it is wholly out of registry with the fixed electrode 12 and the unit will then be at its minimum capacitance with the piston 16 engaging the end wall 62. The piston 16 can no longer move further to the right and the sets of screw threading bind to prevent further rotation of the drive shaft 32 in the same direction.

In moving the piston 16 back towards its extended position, the drive shaft 32 is turned in the opposite direction. Because of the difference in tension between the screws 1'34 and 136, the intermediate cylinder 30 at first turns with the drive shaft '32, advancing the piston 16 longitudin-ally towards the left until its end wall bordering the circular opening 18 engages the enlarged end portion 34 of the intermediate member 30. The intermediate member 30 is now restrained from rotating, and the drive shaft 32 turn Within the intermediate member 30 moving the latter to the left until the piston 16 is carried to its fully extended position. In this position the enlarged terminal extension 46 of the drive shaft 32 engages the end shoulder 38 of the intermediate cylinder 30' halting further outward movement.

It is to be understood that the relative tightness of the screws 134 and 136 may be reversed, in which case the intermediate member 30 will first travel longitudinally and then the piston 16 will travel.

Very fine turning is achieved by use of very fine threading over large total distances achieved thnough the telescoping threading action of the piston 16, intermediate cylinder 30 and drive shaft 32, even though there is only a relatively short longitudinal movement of the piston. At the same time the drive shaft 32 is always longitudinally immovable and never projects from the exterior of the condenser body but is retained within the recess 68. Thus, the overall size of the unit is considerably reduced and the unit may be easily installed.

The elliptical shape of the piston 16 body 10 prevents the piston from turning during ment even though the piston may fit somewhat freely in the hollow body 10. Therefore, manufacture of this device is facilitated since tight tolerances are not needed. Further, this provides a finer and more accurate adjustment of capacitance. In addition, the elliptical shape of these parts provides for greater electrode areas than would be afforded by circular shape with a consequent increase in capacity.

It is further to be understood that the ing the cylindrical member 96 sures against any backlash and the head piece 62 is maintained in an always accessible position with the slot 54 easily reached by the screw driver blade or suitable tool used for adjustment.

To disassemble the trimmer capacitor from the panel,

spring 106 urgover the split thimble asonly the not 114 need be removed and the tor can then be removed from the panel. To disassemble the trimmer capacitor, nut 74 is unscrewed d head piece 52 is removed permitting the spring 106, cylindrical member 96 and the split thimble to be taken off the shaft 32 after which the entire shaft is pushed into the hollow body for removal, as may be desired.

It is to be understood that in lieu of the elliptical shaped blody, various other shapes such as oval or the like may be employed and various manufacturing expedience may be resorted to to facilitate mass production of this adjustable electrical reactance unit. The use of other than a circular shaped body serves to permit longitudinal motion of the piston 16 in the body while preventing relative rotation. Further, the elliptical shape affords other advantages, particularly with respect to electrical values.

Since from the foregoing the construction and advantages of this trimmer capacitor are readily understandable, further description is believed to be unnecessary.

However, since numerous modifications may be readily resorted to by those skilled in the art, it is intended that the claims appended hereto be construed broadly and in a manner consistent with the spirit and scope of this invention.

What I claim is:

1. An adjustable electrical reactance unit comprising a hollow body having a longitudinal bore, a piston slidably and non-rotatably mounted in said hollow body, drive means for moving said piston longitudinally in said hollow body, said hollow body including an end wall having an opening therein, said drive means including a drive shaft extending through said opening and threadedly coupled to said piston, said end wall having an externally threaded extension and having a recess therein, said shaft extending into said recess, a split thimble in said recess non-rotatably and non-slidably fixed about said shaft and having a portion engaging said end wall to shaft in said recess, wedge means surrounding said thimble for holding said thimble in position, a drive head secure-d to said shaft, means retaining said drive head in said recess and a spring yieldingly engaging said drive head and said wedge means for retaining said split thimble on said shaft and for preventing lost motion, and

trimmer capacimentary to said truncated conical section for sliding thereover to hold said split thimble together.

3. An adjustable electrical reactance unit according to claim 1, wherein said cylindrical member is provided with an external flange, said spring engaging said flange.

4. An adjustable electrical reactance unit comprising a hollow body having a longitudinal bore, a piston slidably and non-rotatably mounted in said hollow body, said hollow body including an end Wall, drive means for moving the piston longitudinally in said housing, said piston having an internally threaded cylindrical bore, said drive means including an intermediate member having external threading meshing with the internally threaded piston bore for telescoping movement of said intermediate low body, external threading on said drive shaft meshing with the internally threaded bore of said intermediate member for telescoping movement of said drive shaft when said drive shaft is rotated, said intermediate member connecting said drive shaft to said piston, said end wall having an externally threaded extension and having a recess therein, said drive shaft extending into said recess, a split thimble in said recess non-rotatably and nonhold said I slidably fixed about said shaft and having a portion engaging said end wall to retain said drive shaft in said recess, wedge means surrounding said thimble for holding said thimble in position, a drive head secured to said shaft, means retaining said drive head in said recess, and a spring yieldingly engaging said drive head and said wedge means for retaining said split thimble on said shaft and for preventing lost motion, and a nut threadedly secured on said end wall extension.

5. An adjustable electrical reactance unit comprising a hollow body having a longitudinal bore, a piston slidably and non-rotatabl'y mounted in said hollow body, drive means for moving said piston longitudinally in said hollow body, said hollow body including an end wall having an opening therein, said drive means including a drive shaft extending through said opening and threadedly coupled to said piston, said end wall having an externally threaded extension and having a recess therein, said shaft extending into said recess, a split thimble in said recess, said split thimble being non-rotatably and non-slidably fixed about said shaft and having a portion engaging said end wall to hold said shaft in said recess while preventing lost motion, wedge means surrounding said thimble for holding said thimble in position, and a nut threadedly secured on said end wall extension.

6. An adjustable electrical reactance unit comprising a hollow body having a longitudinal bore, a piston slidably and non-rotatably mounted in said hollow body, said hollow body including an end wall, drive means for moving the piston longitudinally in said housing, said piston having an internally threaded cylindrical bore, said drive means including an intermediate member having external threading meshing with the internally threaded piston bore for telescoping movement of said intermediate member with said piston when said intermediate member is rotated, said intermediate member also having an internally threaded cylindrical bore, a drive shaft journalled in said end wall and extending longitudinally of said hollow body, external threading on said drive shaft mesh ing with .the internally threaded bore of said intermediate member for telescoping movement of said drive shaft when said drive shaft is rotated, said intermediate mem ber connecting said drive shaft to said piston, said end wall having an externally threaded extension and having a recess therein, said drive shaft extending into said recess, a split thimble in said recess non-rotatably and non-slidably fixed about said shaft and having a portion engaging said end wall to retain said drive shaft in said recess, wedge means surrounding said thimble for holding said thimble in position, and a nut threadedly secured on said end wall extension.

7. An adjustable electrical resistance unit according to claim 6, wherein said split thimble is provided with a truncated conical section, said wedge means including a cylindrical member having an internal portion complementary to said truncated conical section for sliding thereover to hold said split thimble together.

8. A variable electrical reactance unit according to claim 4 which also includes stop means for limiting longitudinal and turning movement of said intermediate member relative to said drive shaft and relative to said piston.

9. A variable electrical reactance unit according to claim 6 wherein said intermediate member and said drive shaft each have friction means for adjustably varying the friction between the external threading on the intermediate member and the internally threaded piston bore and between the external threading on the drive shaft and the internally threaded intermediate member bore respectively.

10. A variable electrical reactance unit according to claim 9 in which said friction means comprises a transverse slot in said intermediate member and drive shaft extending through the internal threading thereof, and a respective screw engaging each of said slots for spreading apart the respective threading through which said slot.

extends.

11. A variable electrical reactance unit according to claim 10 wherein said split thimble is provided with a truncated conical section, said wedge means including a cylindrical member concentrically disposed about said split thimble and said drive shaft, said cylindrical member having an internal portion complementary to said truncated conical section for sliding thereover to hold said split thimble together.

12. A variable electrical resistance unit according to claim 11, further including a drive head secured to said drive shaft, means retaining said drive head in said recess, a flange on said cylindrical member, and a spring yieldingly engaging said flange and said drive head for urging said cylindrical member into wedging engagement with sfiidk split thimble to retain said split thimble on said drive 5 a t.

References Cited in the file of this patent UNITED STATES PATENTS 

1. AN ADJUSTABLE ELECTRICAL REACTANCE UNIT COMPRISING A HOLLOW BODY HAVING A LONGITUDINAL BORE, A PISTON SLIDABLY AND NON-ROTATABLY MOUNTED IN SAID HOLLOW BODY, DRIVE MEANS FOR MOVING SAID PISTON LONGITUDINALLY IN SAID HOLLOW BODY, SAID HOLLOW BODY INCLUDING AN END WALL HAVING AN OPENING THEREIN, SAID DRIVE MEANS INCLUDING A DRIVE SHAFT EXTENDING THROUGH SAID OPENING AND THREADEDLY COUPLED TO SAID PISTON, SAID END WALL HAVING AN EXTERNALLY THREADED EXTENSION AND HAVING A RECESS THEREIN, SAID SHAFT EXTENDING INTO SAID RECESS, A SPLIT THIMBLE IN SAID RECESS NON-ROTATABLY AND NON-SLIDABLY FIXED ABOUT SAID SHAFT AND HAVING A PORTION ENGAGING SAID END WALL TO HOLD SAID SHAFT IN SAID RECESS, WEDGE MEANS SURROUNDING SAID THIMBLE FOR HOLDING SAID THIMBLE IN POSITION, A DRIVE HEAD SECURED TO SAID SHAFT, MEANS RETAINING SAID DRIVE HEAD IN 